Disposable absorbent articles for receiving and retaining bodily discharges such as urine, feces or menses are well known in the art. Examples of these include disposable diapers, training pants, adult incontinence articles and sanitary napkins.
An important component of disposable absorbent articles is the absorbent core structure. The absorbent core structure typically includes absorbent polymer material, such as hydrogel-forming polymer material, also referred to as absorbent gelling material, AGM, or super-absorbent polymer, SAP. This absorbent polymer material ensures that large amounts of bodily fluids, e.g. urine or menses, can be absorbed by the absorbent article during its use and be locked away, thus providing low rewet and good skin dryness.
Traditionally, the absorbent polymer material is incorporated into the absorbent core structure with cellulose or cellulosic fibres. However, over the past years, significant effort has been spent to make thinner absorbent core structures which can still acquire and store large quantities of discharged body fluids, in particular urine. Hereto, it has been proposed to reduce or eliminate these cellulose fibres from the absorbent core structures. To maintain the mechanical stability of the absorbent core structures, small quantities of thermoplastic adhesive material, such as fibrous thermoplastic adhesive material, are added to stabilize the absorbent polymer material. Thus, absorbent structures having the required permeability/porosity, reduced gel-blocking, and that form stable structures in use or transport are provided.
However, during the course of these developments, it has been observed that in some instances, such as after extended storage periods or storages at high temperature, the absorption speed may be reduced when the absorbent polymer material is incorporated into absorbent structures with certain thermoplastic adhesive materials. The inventors found that this may be due to the interactions of certain components of the adhesive thermoplastic material with the surface of the absorbent polymer material. Thermoplastic adhesive materials typically comprise one or more thermoplastic polymer in combination with other thermoplastic diluents, such as tackifying resins, plasticizers and other additives such as antioxidant. Plasticizers are typically compounds of low molecular weight (<2000 g/mole) including mineral oils or organic oils, all together referred herein as “oily substances”. Examples of mineral oils include paraffinic oils, naphthenic oils and aromatic oils. The inventors found that with time and/or temperature, these oily substances may tend to partially separate from the thermoplastic adhesive material and migrate through the absorbent structure in the direction of the absorbent polymer material, thus rendering the surface of the absorbent polymer material more hydrophobic, and thereby reducing the affinity of the surface with hydrophilic materials such as urine, thereby leading to an overall loss of performance. The loss of performance resulting from the migration of some of the components of the thermoplastic adhesive material may be compensated by the addition of more absorbent polymer materials which is particularly costly.
Therefore, there is still a need to overcome the negative impact that separation and migration of some components of the thermoplastic adhesive material may have on the performances of the absorbent structure in order to provide absorbent structures/absorbent articles which perform satisfactory when thermoplastic adhesive material is added to the absorbent polymer material.